1. Field of the Invention
The present invention relates generally to the field of holography. More particularly, the present invention relates to a direct-to-digital hologram acquisition and replay system (i.e., no film, no plates). In a preferred implementation of the present invention, the hologram acquisition is based on a charge coupled device (CCD) camera. The present invention thus relates to a holographic system.
2. Discussion of the Related Art
Traditional methods of holography have used film or holographic plates (glass plates with a photographic emulsion optimized for holography) to record the hologram..sup.(1) Replay has only been possible using lasers (or in some cases white light) and the original recorded hologram or a duplicate of it, in an analog method. These analog methods are slow, cumbersome, and expensive..sup.(4) There is also no way to reduce them to electronic signals that can be transmitted and replayed at another location. It is always necessary to send hard copy. Worse still, the time delay involved in processing the film prevents the use of holography and its variants in many situations. Even if the expense of the classical holographic system itself was tolerable, the time delay and low throughput caused by the necessity of processing the film, introduces expenses associated with the delay that are absolutely intolerable (e.g., a tire manufacturer cannot wait 45 minutes, or even two minutes, to know that a particular tire has a flaw in it).
Referring to FIG. 1, a classical side-band holography system recordation geometry is shown..sup.(2-3) Light from a laser 110 is expended by a beam expander 120. After passing through a lens 130, the light is split into two components by a beamsplitter 140. The beamsplitter 140 can be, for example, 90% reflective. The reflected beam constituting an object beam 150 travels toward and is reflected by a mirror 160. The object beam 150 then travels toward an object 170. The object beam 150 is then incident upon a holographic plate 190.
Meanwhile, that portion of the light from lens 130 that is transmitted through the beamsplitter 140 constitutes a reference beam 180 that travels toward and is reflected by a mirror 200. The reflected reference beam is then incident upon the holographic plate 190.
More recently, holographic interferometry has been developed, albeit also as an analog method..sup.(5) This has included the development of focussed holography..sup.(6-7)
Within this application several publications are referenced by superscripts composed of arabic numerals within parentheses. Full citations for these, and other, publications may be found at the end of the specification immediately preceding the claims. The disclosures of all these publications in their entireties are hereby expressly incorporated by reference into the present application for the purposes of indicating the background of the present invention and illustrating the state of the art.